Vehicular engines typically employ a front engine accessory drive to transfer power to one or more accessories, such as an alternator, an air conditioner compressor, a water pump and various other accessories. Many different types of tensioner have been proposed throughout the history of internal combustion engines so as to maintain tension in the belt that is used to transfer the power to the accessories. Some tensioners are configured to impart a very high belt tension on the belt in order to ensure that, in all the modes of operation of the engine and accessories, a situation does not occur where the belt slips on one or more of the pulleys that it is engaged with. It would be advantageous to provide a tensioner that can maintain high belt tension when desired, but lower belt tensioner when a high belt tension is not needed. It would further be advantageous to be able to provide such a tensioner with relatively little complexity and at relatively low cost.